Liquid crystal displays are used as flat-screen display apparatuses. In the liquid crystal displays, a backlight that irradiates an entire surface of a liquid crystal panel from the back is used, and the liquid crystal displays can be roughly classified into a direct type and an edge-light type depending on structures of the backlights. Since light enters from a side surface of a light guide plate to be emitted uniformly from an upper surface of the light guide plate to the liquid crystal panel in the edge-light type, there has been a drawback that it becomes more difficult to illuminate the entire panel uniformly with high luminance as the display becomes larger. Therefore, a backlight of a current large-size display is provided with a plurality of fluorescent lamps to obtain desired characteristics (see, for example, Patent Document 1).
Incidentally, in recent years, aiming at additionally reducing a thickness and weight, prolonging a lifetime, and reducing an environmental load of backlights of large-size displays and also at improving moving-image characteristics by flash control, using a light-emitting diode as a light source is attracting attention. In a case of emitting white light to illuminate a liquid crystal panel in such a backlight that uses a light-emitting diode, the following two methods are used.
The first method is a method that uses light-emitting diodes of three colors of R, G, and B and involves combining light of the light-emitting diodes of three colors of R, G, and B by lighting them up at the same time to thus obtain white light. The second method is a method that uses a blue-color light-emitting diode chip 25 as a light-emitting device as shown in FIG. 20. This method involves covering a circumference of the blue-color light-emitting diode chip 25 with a phosphor-containing resin 42 to thus convert blue light from the blue-color light-emitting diode chip 25 into white light.
Moreover, it is also possible to adopt a structure in which a phosphor sheet 21 is provided between blue-color light-emitting diodes 10 and a liquid crystal panel (not shown) while being apart from the blue-color light-emitting diodes 10 as shown in FIG. 21, instead of covering the circumference of the blue-color light-emitting diode chip with the phosphor-containing resin.
Further, in recent years, there is proposed a method of controlling emission luminance of an entire backlight based on display luminance information of an entire display screen. Furthermore, there is also proposed a method of dividing a display screen into a plurality of areas (hereinafter, each area will be referred to as “segment”) in association with light sources constituting a backlight and partially suppressing emission luminance of the light source in association with display luminance necessary for each of the segments (see, for example, Patent Document 2).
It should be noted that the “emission luminance” described above refers to luminance at a time light is emitted from the light sources, and the “display luminance” described above refers to luminance at a time light emitted from the light sources transmits through a display portion (display screen).
FIG. 22 conceptually show an example of such a control method. For example, in a case where an image 52 in which a brightest oval 51 is displayed at substantially a center portion and an area around the oval 51 is dark is displayed as shown in FIG. 22(A), assuming that a backlight of a liquid crystal display apparatus on which such an image 52 is displayed is divided longitudinally and laterally into a plurality of segments 11 as shown in FIG. 22(B), emission luminance of a segment corresponding to a spot having lowest display luminance is suppressed as shown in FIG. 22(C) when displaying the image 51 shown in FIG. 22(A). Here, 11-a, 11-b, and 11-c are segments whose emission luminance is not suppressed, and segments other than 11-a, 11-b, and 11-c are segments whose emission luminance is suppressed. By thus displaying an image while partially suppressing emission luminance of the backlight, it is possible to prevent the backlight from being lit wastefully, with the result that power consumption can be reduced.    Patent Document 1: Japanese Patent Application Laid-open No. 2005-108635    Patent Document 2: Japanese Patent Application Laid-open No. 2004-212503